Thin film magnetic heads are used extensively in data processors, such as disk drives. A typical thin film head comprises, inter alia, a nonmagnetic ceramic substrate, first and second magnetic layers typically made of Permalloy (Nife) that form a yoke, and an electrically conductive coil. The magnetic flux that is generated in the yoke interacts with current in the conductive coil to effectuate transducing of data signals during write and read modes. Conventionally, the first magnetic yoke layer P1 is formed as a substantially planar layer above the substrate and the second magnetic yoke layer P2 is configured in spaced relation above the P1 layer with the electrical coil interposed between the two magnetic layers. An insulating photoresist epoxy surrounds the coil to prevent electrical shorting between the conductive coil and the Permalloy layers. A via or through hole is provided to allow contact between the P1 layer and the P2 layer to form a closure and a thus a substantially continuous magnetic path. An insulating layer provides a transducing gap between two pole tips at the ends of the P1 and P2 magnetic layers of the yoke structure which interfaces with a magnetic medium during reading and recording of data signals.
One problem that is experienced when operating with thin film heads is head relaxation noise, also known as popcorn noise, which is associated with the magnetic domains inherent in the yoke material. This noise manifests itself as noise spikes which adversely affect the data signal being processed. The level of noise is in proportion to the length of the domain wall that is collinearly aligned with the electrical coil turns. Popcorn noise and possibly wiggle (domain instability) are caused by thermal rise during writing in the cross-linked photoresist epoxy through mismatch of the expansion coefficients of Permalloy and of the cross-linked epoxy whose thermal expansion coefficients are 12.5.times.10.sup.-6 /.degree. C. and 50.times.10.sup.-6 /.degree. C. respectively. Also there is a mismatch of the Permalloy expansion coefficient with that of the slider material, which typically is titanium carbide (TiC) or alumina (Al.sub.2 0.sub.3), and with the Al.sub.2 0.sub.3 overcoat or cap layer of the thin film head.
Constant efforts have been made to reduce the noise problem and improve head operating efficiency. In an abstract delivered at the Intermag Conference in Pittsburgh in April, 1991, entitled "A Study of Popcorn Noise for Thin Film Heads", K. Morikawa et al. describe an approach for decreasing popcorn noise by narrowing the width of the yoke and/or changing the Fe composition of the magnetic Fe-Ni material used in the yoke. Another article that discusses noise relaxation in thin film heads is found in an abstract by K. B. Klassen et al., IEEE Trans. Magn. MAG-25, 3212-3214 (1989). These prior art thin film heads still experience a significant level of popcorn noise and are characterized by a relatively high inductance which adversely affects the signal being processed through the heads. It is highly desirable to reduce the degrading popcorn noise and thus improve the signal-to-noise ratio.